Editing/removing a frame section without it going crazy?

I disagree.

At first use menu: Object --> Expand Appearance

All Pathfinder operations should then be available.

Sidenote:

If you're trying something else, take a hard look at the "open endpoints".

Adding 2 points to the path where you want a gap, direct select the segment inbetween and choosing Clear would have done it without Pathfinder.

sorry i wasnt clear because it was very late, the image is for gold foil printing so i think would need all gold lines on one layer with sections missing in the frame.

this is what happens when i edit a section of the frame with the knife tool or eraser

Without knowing how this is put together, I just covered what I wanted to get rid of.

Can you please show a screenshot of your Layers panel with the disclosure arrows twirled open so we can see how this is put together?

Thanks,
Peter